Sonoluminescence is a well-known phenomena discovered in the 1930's in which light is generated when a liquid is cavitated. Although a variety of techniques for cavitating the liquid are known (e.g., spark discharge, laser pulse, flowing the liquid through a Venturi tube), one of the most common techniques is through the application of high intensity sound waves.
In essence, the cavitation process consists of three stages; bubble formation, growth and subsequent collapse. The bubble or bubbles cavitated during this process absorb the applied energy, for example sound energy, and then release the energy in the form of light emission during an extremely brief period of time. The intensity of the generated light depends on a variety of factors including the physical properties of the liquid (e.g., density, surface tension, vapor pressure, chemical structure, temperature, hydrostatic pressure, etc.) and the applied energy (e.g., sound wave amplitude, sound wave frequency, etc.).
Although it is generally recognized that during the collapse of a cavitating bubble extremely high temperature plasmas are developed, leading to the observed sonoluminescence effect, many aspects of the phenomena have not yet been characterized. As such, the phenomena is at the heart of a considerable amount of research as scientists attempt to further characterize the phenomena (e.g., effects of pressure on the cavitating medium) as well as its many applications (e.g., sonochemistry, chemical detoxification, ultrasonic cleaning, etc.).
U.S. Pat. No. 4,333,796 discloses a cavitation chamber that is generally cylindrical although the inventors note that other shapes, such as spherical, can also be used. It is further disclosed that the chamber is comprised of a refractory metal such as tungsten, titanium, molybdenum, rhenium or some alloy thereof and the cavitation medium is a liquid metal such as lithium or an alloy thereof. The chamber is heated to a temperature greater than the melting temperature of the selected cavitation medium. The cavitation medium within the chamber does not completely fill the chamber, thus leaving a vapor-liquid interface within the chamber. The ambient pressure within the chamber is the hydrostatic pressure plus the gas pressure maintained above the vapor-liquid interface and the vapor pressure of the medium itself. In at least one disclosed embodiment, the desired gas pressure is obtained by coupling the chamber to an external source of deuterium. Projecting through both the outer housing and the cavitation chamber walls are a number of acoustic horns, each of the acoustic horns being coupled to a transducer which supplies the mechanical energy to the associated horn.
U.S. Pat. No. 4,563,341, a continuation-in-part of U.S. Pat. No. 4,333,796, discloses a slightly modified, cylindrical cavitation chamber. The chamber is surrounded by an external heating coil which allows the cavitation liquid, e.g., aluminum, within the chamber to be maintained at the desired operating temperature. The system is degassed prior to operation by applying a vacuum through a duct running through the cover of the chamber. During operation, a vapor-liquid interface is maintained within the chamber. Argon gas is admitted to the chamber through the duct in the cover of the chamber, thus allowing the operating pressure to be controlled.
U.S. Pat. No. 5,659,173 discloses a sonoluminescence system that uses a transparent spherical flask fabricated from Pyrex®, Kontes®, quartz or other suitable glass and ranging in size from 10 milliliters to 5 liters. The inventors disclose that preferably the liquid within the flask is degassed and the flask is sealed prior to operation. In one disclosed embodiment, the cavitation chamber is surrounded by a temperature control system, thus allowing the liquid within the chamber to be cooled to a temperature of 1° C. Techniques are disclosed to control the static pressure in the liquid, for example coupling the chamber to a piston or latex balloon. Bubbles are introduced into the cavitation fluid using a variety of techniques including dragging bubbles into the fluid, for example with a probe, and localized boiling.
U.S. Pat. No. 5,858,104 discloses a shock wave chamber partially filled with a liquid. The remaining portion of the chamber is filled with gas which can be pressurized by a connected pressure source. Acoustic transducers mounted in the sidewalls of the chamber are used to position an object within the chamber while another transducer delivers a compressional acoustic shock wave into the liquid. A flexible membrane separating the liquid from the gas reflects the compressional shock wave as a dilatation wave focused on the location of the object about which a bubble is formed.
U.S. Pat. No. 5,968,323 discloses a cavitation chamber filled with a low compressibility liquid such as a liquid metal. A sealed fluid reservoir is connected to the bottom of the cavitation chamber by a pipe. Both the chamber and the reservoir are contained within a temperature controlled container. By pressurizing or evacuating the reservoir, fluid can be forced into or withdrawn from the cavitation chamber. Fluid flow into or out of the chamber is aided by a vacuum pump and a pressurized gas source coupled to the top of the cavitation chamber. The system includes two material delivery systems for introducing materials or mixtures of materials into the chamber. One of the delivery systems is coupled to the bottom of the chamber and is intended for use with materials of a lower density than that of the cavitation liquid, thus causing the material to float upwards. The second delivery system is coupled to the top of the chamber and is intended for use with materials of a higher density than that of the cavitation liquid, thus causing the material to sink once introduced into the chamber.
PCT Application No. US02/16761 discloses a nuclear fusion reaction chamber which is partially filled with the desired cavitation fluid, such as deuterated acetone. Within the chamber are upper and lower members, preferably anchored to the chamber, that define a resonant cavity. In at least one disclosed embodiment, the chamber and upper/lower members are all fabricated from glass. The chamber volume above the cavitation fluid is evacuated to approximately the vapor pressure of the cavitation fluid. In a preferred embodiment, a refrigeration device maintains the reaction chamber at a sub-ambient temperature. In at least one disclosed embodiment, acoustic waves are used to pretension the liquid. After the desired state of tension is obtained, a cavitation initiation source, such as a neutron source, nucleates at least one bubble within the liquid, the bubble having a radius greater than the critical bubble radius. The nucleated bubbles are then imploded, the temperature generated by the implosion being sufficient to induce a nuclear fusion reaction.
In an article entitled Ambient Pressure Effect on Single-Bubble Sonoluminescence by Dan et al. published in vol. 83, no. 9 of Physical Review Letters, the authors used a piezoelectric transducer to drive cavitation at the fundamental frequency of a glass cavitation chamber. This apparatus was used to study the effects of ambient pressure on bubble dynamics and single bubble sonoluminescence.
A variety of cavitation systems have been designed, many of which utilize partially filled cavitation chambers. As a result of the free liquid interface, it is often difficult to achieve the desired pressure within the cavitation fluid, especially if the cavitation fluid has a high vapor pressure. The present invention overcomes this problem.